An investigation of thermal stimulation in intact teeth P. Linsuwanont, J.E.A. Palamara, H.H. Messer * School of Dental Science, The University of Melbourne, 720 Swanston Street, Melbourne, Victoria 3010, Australia 1. Introduction The sensory response of teeth to thermal stimuli has been studied for decades. Ultrastructural studies have shown that dentinal tubules contain the odontoblast process and non- myelinated terminals of sensory nerves. These sensory nerves extend approximately 100 mm into the tubules from the pulp and have been found to lie in close association with odontoblast processes. 1 It seems reasonable to assume that these receptors are the first sensory structures to be affected by thermal stimuli. According to the hydrodynamic hypothesis, the contents of dentinal tubules act as hydraulic linkages between the external environment and the pulpal nerve endings. 2 Stimuli applied to the teeth cause displacement of the tubular contents, which in turn excites the nerve terminals. Many ex vivo studies have shown that a cold stimulus causes outward fluid movement (away from the pulp), and a hot stimulus causes inward fluid movement (toward the pulp). 3,4 It was proposed that fluid flow through dentinal tubules is part of the mechanism involved in the transduction of pain- producing stimuli in teeth. Moreover, it has been found that the rate of fluid movement is not constant, and an initially more rapid movement is critical to nerve stimulation. Rapid fluid movement will result in a greater hydrodynamic force which in turn is sufficient to trigger a nerve impulse. 3–5 The rate of fluid flow caused by the application of thermal stimuli is capable of triggering the intradental A fibres in cat teeth. 6,7 archives of oral biology 52 (2007) 218–227 article info Article history: Accepted 7 October 2006 Keywords: Thermal stimulation Intact teeth Dentinal fluid Tooth deformation abstract Objectives: To investigate the response of extracted intact teeth to thermal stimulation in terms of fluid movement, in relation to temperature change within tooth structure. Methods: Dentinal fluid movement was measured in response to thermal stimuli applied to enamel. Freshly extracted teeth with intact crowns were investigated for the effects of thermal stimulation; namely, hot water (80 8C), iced water (2 8C) and carbon dioxide dry ice (72 8C) for 5 s application. Two capillary-based methods were used to measure fluid flow. To measure temperature changes at the dentino-enamel junction (DEJ) and pulpal wall in response to the same stimuli, fine J type thermocouples were used. Results: Thermal stimuli caused fluid movement, which occurred before the temperature changed at the pulp wall. Sealing the dentinal tubules resulted in a delayed response time. In general, fluid movement occurred coincident with the temperature change detected at the DEJ. However, many teeth showed a ‘‘bidirectional’’ response to thermal stimulation. The initial fluid movement in the bidirectional response was detected before the earliest temperature change observed at the DEJ, and was in the opposite direction to the main fluid movement. Conclusion: Our results imply that thermal contraction and expansion of dentinal fluid may not be the complete explanation for dentinal fluid movement in intact teeth. Enamel may serve not only as a temperature transfer medium but may also expand or contract when subjected to thermal stimulation. # 2006 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +61 3 9341 1472; fax: +61 3 9341 1595. E-mail address: hhm@unimelb.edu.au (H.H. Messer). available at www.sciencedirect.com journal homepage: www.intl.elsevierhealth.com/journals/arob 0003–9969/$ – see front matter # 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.archoralbio.2006.10.009